1. Field
Various embodiments of the invention pertain to wireless communication systems. At least one embodiment of the invention pertains to a system and method of transferring communications from a first base station to a second base station from a mobile communication device using a directional antenna.
2. Background
Wireless communication networks enable communication devices to transmit and/or receive information while on the move. These wireless communication networks may be communicatively coupled to other public or private networks to enable the transfer of information to and from the mobile communication devices. Such communication networks typically include a plurality of base stations which provide wireless communication links to mobile communication devices. The base stations may be stationary (e.g., fixed to the ground) or mobile (e.g., mounted on satellites, etc.) and positioned to provide wide area coverage as the mobile communication device travels across different coverage areas.
As a mobile communication device moves around, its communication link with a base station may degrade. In this situation, the communication device switches or connects with another base station for a better quality communication link while its first link is still active. This process of establishing a communication link with another base station is referred to as a “handoff”. The handoff process typically faces the problem of maintaining a reliable communication link with the wireless communication network while switching base stations. Soft handoffs and hard handoffs are two commonly used types of handoffs. A soft handoff is one where a new communication link with a new base station is established before the existing communication link is terminated. In a hard handoff, an existing communication link is typically terminated before a new communication link is established.
Some mobile communication devices may utilize a directional or adaptive antenna. Directional and/or adaptive antennas are typically used to direct signal transmissions in a desired direction. These types of antennas have many advantages over omni-directional antennas when used in modern communications systems. These advantages occur for both transmission and reception of information-bearing signals. During transmission, the directional concentration of radiated energy beam towards a receiver significantly increases the amount of received power per unit of transmitted power. This generally improves the throughput rate of the transmitter-to-receiver link and allows higher rates of information transfer. Furthermore, in interference-limited systems the concentration of power towards the intended receiver reduces the interference caused by the transmitter to the rest of the system, hence increasing its overall capacity. However, performing an efficient handoff using an adaptive or directional antenna has several challenges since directional beams make it difficult to switch between receivers (e.g., base stations) while maintaining a reliable link at the same time.